1. Field of the Invention
The present invention relates to a sensor, and more particularly to a gas sensor including an oxygen sensor, an NOx sensor and an HC sensor for detecting the concentration of a specific gas component in an exhaust gas discharged, from an internal combustion chamber, or a temperature sensor for detecting the temperature of an exhaust gas.
2. Description of the Related Art
Sensors are generally used for controlling the air-fuel ratio of a motor vehicle engine, and include a sensor element having electrical properties which change in accordance with the concentration of a specific gas component in the engine exhaust gas (e.g., JP-A-2007-47093). FIG. 18 shows such a gas sensor (hereinafter, also referred to as a sensor) 1. For example, the gas sensor 1 includes a sensor element (hereinafter also referred to as an element) 21 made of a solid electrolyte having oxygen ion conduction properties, a metal shell (a shell main body) 11 for holding the sensor element 21, and a metallic protective sleeve (an outer sleeve) 81 provided on a rear end (an upper end in the figures) side of the metal shell 11. A terminal surrounding member (also referred to as a separator) 70 is disposed within the protective sleeve 81. As used herein, a “rear end” denotes an upper end of the sensor or components thereof, and a “front end” denotes an opposite end (a lower end) thereof.
In the sensor 1 configured as described above, the terminal surrounding member 70 is made of an electrically insulating material such as a ceramic. As shown in FIG. 18, the terminal surrounding member 70 has terminal holes (hereinafter, also referred to as holes) 75 extending straight in a front-rear direction. Terminal metal fittings 51 are positioned and accommodated in the holes 75, and the holes 75 are partitioned so as to ensure electrical insulation not only between an inner surface of the protective sleeve 81 and the terminal metal fittings 51 but also between the terminal metal fittings 51 (see FIG. 19). Each of the terminal metal fittings 51 includes a terminal connecting portion 53 as a plate spring disposed at a front end of the terminal metal fitting 51. The terminal connecting portions 53 are pressed against respective electrode terminals 25 in the holes 75 by the spring characteristic of the terminal connecting portion 53. The electrode terminals 25 are provided on side surfaces 24 of the element 21 positioned at a center of the terminal surrounding member 70. Accordingly, the terminal metal fittings 51 are electrically connected to respective electrode terminals 25. The terminal metal fittings 51 are connected to front ends (core wire portions) of lead wires 61 by crimping clamp portions (barrels) 57 which extend from the terminal connecting portions 53 by way of relay wire portion 55 to thereby be positioned at the rear ends thereof. The individual lead wires 61 are passed through a sealing elastic member 101 disposed within the protective sleeve 81 and pulled outside the sensor.
In the sensor 1, the sensor element 21 has a long flat plate-like (strip-like) shape. Also, for example, three electrode terminals 25 are provided side by side on one of opposing side surfaces (two facing main plate surfaces) 24, 24 of a portion of the sensor element 21 which lies near its rear end or a rear portion thereof. In the same figure, two terminal electrodes 25 are provided side by side on the other (opposite) side surface 24. On the other hand, the individual terminal metal fittings 51 are disposed within the holes 75 which are formed side by side and partitioned in the terminal surrounding member 70 so as to correspond to the electrode terminals 25, and the terminal connecting portions 53 are pressed against corresponding electrode terminals 25 on the element 21 so as to make electrical connections by virtue of their spring characteristics (see FIG. 18). In this sensor 1, the clamping portion 57 of each terminal metal fitting 51 clamps the front end of the lead wire by a crimping piece 58 that is bent towards the element 21 (an axis G in FIG. 18).
As described above, in the sensor 1, the terminal metal fittings 51 are disposed in the holes 75 which are formed side by side in the terminal surrounding member 70 (see FIG. 19). Consequently, the lead wires 61, which are connected to respective clamping portions 57 at the rear ends of the terminal metal fittings 51, are led out so as to extend in the rear direction in a similar side-by-side arrangement to that of the clamping portions 57. Because of this, the through holes 105 in the sealing elastic member 101, through which the lead wires 61 are passed, open in an arrangement corresponding to the arrangement of the holes 75 shown in FIG. 19 when viewed from the direction of the axis G (a rear end of the sensor).
On the other hand, the sealing elastic member 101 is disposed within the sealing sleeve portion 83 positioned at a rear portion of the protective sleeve 81. In order to ensure a good seal, the sealing sleeve portion 83 is crimped so as to be reduced in diameter from an outer circumferential surface thereof. The sealing elastic member 101 ensures sealing within the through holes 105 through which the individual lead wires 61 are inserted by radial compression resulting from the crimping. In the sealing structure of the lead wires 61, the lead wires 61 which are passed through the through holes 105 are preferably compressed equally and effectively. To obtain this result, and based on the fact that the sealing elastic member 101 normally has a circular cross section (a shape when viewed from a rear end side of the sensor), the through holes 105, as shown in FIG. 20, are preferably disposed at equal angular intervals or an interval close thereto on a circumference (an imaginary circumference) which is concentric with the circular shape.
Consequently, as with the sensor 1 shown in FIG. 18 in which three electrode terminals 25 are provided side by side on the one side surface of the element 21, the clamping portion 57 at the rear end of the terminal metal fitting 51 that is connected to a center electrode terminal 25 is preferably provided further to the outside in FIG. 18 (further rightwards in the figure) than the clamping portions 57 at the rear ends of the terminal metal fittings 51 positioned on both sides of the center terminal metal fitting 51. Namely, the clamping portions 57 are preferably arranged in a manner similar to the through holes 105 in the sealing elastic member 101. On the other hand, to secure this arrangement with respect to the center terminal metal fitting 51, the rear end of the clamping portion 57 is eccentrically offset outwards by bending the relay wire portion 55 residing between the terminal connecting portion 53 and the clamping portion 57 into a crank-like shape or by orienting outwards a crimping portion 58 constituting the clamping portion 57.
3. Problems to be Solved by the Invention
When attempting to eccentrically offset the clamping portion 57 at the rear end in an outwards direction, however, a rear portion of the hole 75 formed in the terminal surrounding member 70 in which the center terminal metal fitting 51 is disposed must be bent outwards into a crank-like shape relative to a rear portion so as to match the shape of the terminal metal fitting. This requires the straight hole structure to be modified into a complex structure. When attempting to obtain such a complex structure, however, an interior structure of the terminal surrounding member 70 is also made complex.
To alleviate this problem, one configuration has been proposed in which the terminal surrounding member 70 is divided in a front-rear direction into a front side surrounding member and a rear side surrounding member, and a rear end face of the front side surrounding member abuts a front end face of the rear side surrounding member. When the one terminal surrounding member is made by combining together the two members in the manner described above, since the degree of freedom in designing the structure of the holes therein and the shape and structure of the terminal metal fittings disposed in the holes is enhanced, the aforesaid problem can be solved. Namely, even when the holes are formed so as to extend in a straight line in parallel with the axis, holes provided in the rear side surrounding member may only have to be provided so as to be eccentrically offset outwards to an appropriate degree relative to the holes provided in the front side surrounding member. Moreover, when such a two-part structure is adopted, part of the terminal metal fitting, for example, can be held at an abutting portion between the two separate surrounding portions, thereby making it possible to obtain an advantage of preventing the terminal metal fitting whose part is so held from moving in the front-rear direction.
However, the configuration in which the single terminal surrounding member is made up of the two divided terminal surrounding members involves the following demerit. The terminal surrounding member is made by combining the two members, and therefore, when considering that the sensor is subjected to various types of vibration due to being mounted in a motor vehicle for use, the position of the sensor tends to be unstable when the sensor is disposed within the protective sleeve 81. Namely, when the two-part structure is adopted, there is a risk that the rear side surrounding member moves so as to rotate about an axis thereof relative to the front side surrounding member, or that both the surrounding members move in a lateral direction relative to each other in such a way that the centers of both the surrounding members deviate from each other. Then, when such movement occurs, the terminal metal fittings disposed in the interiors thereof also move accordingly, leading to likely deformation of the terminal metal fittings. In addition, such structure is prone to an electrical connection failure between the terminal metal fittings and the electrode terminals on the element, leading to reduced reliability.